Biodegradation Of Crude Oil Hydrocarbons Research Articles

Biodegradation of crude oil hydrocarbons by a newly isolated biosurfactant producing strain

New bacterial strain BN66 was isolated by selective enrichment, identified as Bacillus cereus and proved to degrade crude oil, together with biosurfactant synthesis. Free and cryogel immobilized Bacillus cereus cells were involved in a crude oil degradation process. The studied strain degraded 93% of the aliphatic fraction for 48 h. We immobilized cells in two types of cryogels synthesized from high molar mass polyacrylamide or acrylamide precursors and explored the degradation capability and possibility for re-use of the preparations. Reusability tests revealed that the oil degradation ability of immobilized cells was stable after 47 days (28 °C and shaker speed 120 rpm) and the degradation rate of immobilized cells was maintained at a high level up to the 20th cycle of operation. The matrices obtained from high molar mass polyacrylamide appeared to be more suitable due to their ability to keep the cells within the carrier. The cells immobilized in cryogels exhibited more effective degradation for 22 active cycles at semicontinuous mode of operation compared to only three cycles performed by free cells.

Total Petroleum Hydrocarbon Degradation by Endophytic Fungi from the Ecuadorian Amazon

The capacity of 133 fungal endophyte isolates for degrading petroleum hydrocarbons was evaluated. The endophytes were isolated from leaf and stem tissues from 23 plants collected in a natural habitat contaminated with crude oil in southwestern Ecuador. Their capacity for hydrocarbon biodegradation was tested by an in vitro colorimetric qualitative test during 10 days, using the Minimal Salt Medium and crude oil as the carbon source. Taxonomic identification of the endophytic fungi that showed bioactivity in the qualitative test was carried out by analysis of the ITS gene of the region 18S of the rDNA. Endophytes showed the best results in the previous qualitative test where selected for a quantitative in vitro test for 30 days. Residual hydrocarbons were tracked by infrared spectroscopy (IR) and gas chromatography (GC) with a flame ionization detector. The maximum removal rates of total petroleum hydrocarbons were 99.6% (IR) and 99.8% (GC), corresponding to fungi of the genus Verticillium sp. and Xylaria sp. 1 respectively. This is the first report of biodegradation of crude oil hydrocarbons by endophytic fungi in a tropical ecosystem. The results suggest these fungal isolates are potential hydrocarbon biodegraders that could be used in bioremediation processes.

Potential of the green alga Chlorella vulgaris for biodegradation of crude oil hydrocarbons

Oil production and/or transportation can cause severe environmental pollution and disrupt the populations of living organisms. In the present study, biodegradation of petroleum hydrocarbons is investigated using Chlorella vulgaris as a green algal species. The microalga was treated by 10 and 20g/l crude oil/water concentrations at two experimental durations (7 and 14days). Based on the results obtained, C. vulgaris owned not only considerable resistance against the pollutants but also high ability in remediation of crude oil hydrocarbons (~94% of the light and ~88% of heavy compounds in 14days). Intriguingly, dry weight of C. vulgaris increased by the rising crude oil concentration indicating the positive effect of crude oil on the growth of the algal species. This biodegradation process is remarkably a continuous progression over a period of time.

Biodegradation and adsorption of crude oil hydrocarbons supported on “homoionic” montmorillonite clay minerals

The role of “homoionic” montmorillonites in hydrocarbon removal during biodegradation was investigated in aqueous clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. The clay mineral used for this study was montmorillonite which was treated with the corresponding metal chloride salt to produce Na-, K-, Mg-, Ca-, Zn-, Al-, Cr-, and Fe-montmorillonites used in this study. The study indicated that Zn- and K-montmorillonites were inhibitory to biodegradation of the crude oil hydrocarbons and appears to do so as a result of extensive adsorption of the hydrocarbons. However, Na-, Ca- and Fe-montmorillonites with relatively high surface area and cation exchange capacity (CEC) were stimulatory to biodegradation of the crude oil hydrocarbons. This study reveals that whereas surface area and the ‘local bridging effect’ were important factors from the clay minerals that conferred stimulatory effect on the biodegradation of the hydrocarbons, the hydrolysis of the interlayer water by trivalent cations of the clay to generate protons and increase acidity of the medium is suggested to be inhibitory to biodegradation of the crude oil hydrocarbons. The interlayer cations (trivalent cations) that impart the highest local bridging effect which is stimulatory to biodegradation also impart the highest hydrolysis of interlayer water which is inhibitory. This study showed that interlayer cations play a crucial role on the ability of the clay mineral to influence biodegradation of the hydrocarbons.

Effect of acid activated clay minerals on biodegradation of crude oil hydrocarbons

The role of acid activated clays and unmodified clays in hydrocarbon removal during biodegradation was investigated in aqueous clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. The clay minerals used for this study were Na-montmorillonite, palygorskite, saponite and kaolinite. The clay mineral samples were treated with hydrochloric acid to produce acid activated clays which were used in this study. The study indicated that acid activated clays and untreated kaolinite were inhibitory to biodegradation of the hydrocarbons via different mechanisms whereas the untreated saponite was neutral to biodegradation of the hydrocarbons. However, untreated palygorskite and Na-montmorillonite were stimulatory to biodegradation and appears to do so as a result of the clays' ability to provide high surface area for the accumulation of microbes and nutrients such that the nutrients are within the ‘vicinity’ of the microbes. Adsorption of hydrocarbons was significant during biodegradation especially with unmodified palygorskite, where there was more than 40% removal of total petroleum hydrocarbons (TPH) by adsorption in the experimental microcosm containing 5:1 ratio (w/w) of clay to oil.

Phylogenetic diversity of dominant bacterial communities during bioremediation of crude oil-polluted soil

Bioremediation of hydrocarbon pollutants is advantageous owing to the costeffectiveness of the technology and the ubiquity of hydrocarbon degrading microorganisms in the soil. Soil microbial diversity is affected by hydrocarbon perturbation thus selective enrichment of hydrocarbon utilizers occurs. Hydrocarbons interact with the soil matrix and soil microorganisms determining the fate of the contaminants relative to their chemical nature and microbial degradative capabilities respectively. Bacterial dynamics in crude oil-polluted soil microcosms undergoing bioremediation were investigated over a 42-day period. Four out of the five microcosms containing 4kg of pristine soil each were contaminated with 4% Arabian light crude oil. Three microcosms were amended with either 25g of NPK fertilizer, calcium ammonium nitrate or poultry droppings respectively while the fourth designated oilcontaminated control was unamended. The fifth microcosm had only pristine soil and was set up to ascertain indigenous bacterial community structure pre-contamination. Biostimulated soils were periodically tilled and watered. Hydrocarbon degradation was measured throughout the experimental period by gas chromatography. Gas chromatographic tracing of residual hydrocarbons in biostimulated soils showed marked attenuation of contaminants starting from the second (day 14) till the sixth (day 42) week after contamination whereas no significant reduction in hydrocarbon peaks was seen in the oil contaminated control soil throughout the 6-week experimental period. Molecular fingerprints of bacterial communities involved in aerobic biodegradation of crude oil hydrocarbons in biostimulated soils and controls were generated with DGGE using PCR-amplification of 16S rRNA gene obtained from extracted total soil community DNA. DGGE fingerprints demonstrated that NPK, calcium ammonium nitrate and poultry droppings selected different bacterial populations during the active phase of oil degradation. Cluster analysis of DGGE bands using simple matching group average setting revealed that poultry droppings-amended soils and calcium ammonium nitrateamended soils formed distinct clades meaning that the treatment selected similar bacterial populations for each of the treatments whereas NPK soils showed less association. Excision, reamplification and sequencing of dominant DGGE bands in biostimulated soils revealed the presence of distinct hydrocarbon degraders like Corynebacterium spp., Dietzia spp., low G+C Gram positive bacteria and some uncultured bacterial clones. Phylogenetic analysis of the 16S rRNA gene sequences of these dominant bacterial communities was conducted using the neighbour joining method of PHYLIP. Two distinct clades appeared in the tree clustered members of the Actinobacteria and Firmicutes separately. The overall data suggested that Gram positive bacteria especially members of the Actinobacteria may have a key role in bioremediation of crude oil-polluted soil.